What are some common Spanish mistakes made by native speakers?

Answer 1

Adding to what Dr. David said, the majority of mistakes I hear from native Spanish speakers are related to grammar. It's very different to grow up just speaking a language compared to actually studying the rules. Along these lines, most native Spanish speakers would not be able to tell you if a verb has been conjugated in the imperative or subjunctive form, or if a verb is a stem-changer. I wouldn't know the majority of these phrases in English had I not studied them in Spanish.

Answer 2

Not using the imperfect subjunctive and conditional tenses correctly in the same sentence. Example: "If I had a million dollars I would buy a nice house." I've heard many native speakers say this "if then" sentence like this. "Si tuviera un million de dolares comprara una casa buena." The correct way to say it is, "Si tuviera un million de dolares compraria una casa buena.